Interest in surface antigens of vascular endothelial cells has come from several lines of research, including studies of lymphocyte homing, inflammation, blood clotting, and tumor metastasis. Exemplary of the vast body of literature in this area are Bevilacqua, Ann. Rev. Immunol. 11:767-804 (1993); Shimizu et al., Immunol. Today 13:106-112 (1992); Zimmerman et al., Immunol. Today 13:93-99 (1993); Butcher et al., Cell 67:1033-1037 (1991); Schlingemann et al., Lab. Invest. 52:71-76 (1985); Schlingemann et al., Am. J. Pathol. 138:1335-1347 (1991); Picker et al., Ann. Rev. Immunol. 10:561-591 (1992); Asborn, Cell 62:3-6 (1990); Roth, Immunol. Today 13:100-105 (1992); Weidner et al., New Eng. J. Med. 324:1-8 (1991). Throughout these studies, monoclonal antibodies (mAbs) have proven to be valuable tools for dissecting the antigenic structure of endothelial cells in different organs, tissues or segments of the vascular system, and the endothelial responses to inflammation, tissue damage, and tumor growth. Furthermore, mAbs have been used in the biochemical and molecular genetic characterization of endothelial antigens and in the functional analyses of endothelial molecules in vitro and in vivo.
Several categories of endothelial antigens have been distinguished, based on their distribution patterns in normal and lesional blood vessels. These include (i) antigens with wide distribution in the vascular system, such as Factor VIII-related antigen (FVIIIRA), PAL-E, and CD13, as per Schlingemann et al., Lab Invest. 52:71-76 (1985); Kuzu et al., J. Clin. Path. 45:143-148 (1992); (ii) antigens restricted to vessels in specific organs or tissues, or to unique histologic types of vessels, as illustrated by vascular addressins and GlyCAM-1; and (iii) inducible antigens, such as E-selectin, VCAM-1, and ICAM-1, that are not present or expressed at low levels in normal endothelium but are upregulated in inflamed tissues in vivo and/or induced or cultured endothelial cells by proinflammatory cytokines, notably tumor necrosis factor (TNF) and interleukin-1 (IL-1) (Pober et al., Lab. Invest. 64:301-305 (1991); Kuzu et al., Lab. Invest. 69:322-328 (1993)).
However, none of the previously identified endothelial antigens serves as a unique endothelial cell lineage marker; i.e., they are either not widely expressed in the vascular system (antigenic heterogeneity) or they are expressed on certain nonendothelial cells. Time and again, when mAbs with apparent specificity for endothelium were subjected to rigorous specificity analyses, including tests with panels of cultured cells that represent diverse cell lineages, and immunohistochemical analysis of fetal and adult normal tissues and lesional tissues, unexpected reactivities and nonendothelial cells were uncovered. Bevilacqua, supra; Shimizu et al., supra; Zimmerman et al., supra; Butcher et al., supra, Kuzu et al., supra; Ruiter et al., J. Invest. Dermatol. 93:25-32 (1989); Gougos et al., Int. Immunol. 4:83-92 (1992); Alles et al., J. Histochem. Cytochem. 34:209-214 (1986). For example, FVIIIRA is present in megakaryocytes and platelets, and CD31, CD36, and CD34 are expressed by subsets of lymphocytes and myelomonocytic cells. Similarly, BW200 is expressed in mesothelium and glomerular epithelium, PAL-E is detected in the epidermis (Ruiter et al., supra); and endoglin is present in placental trophoblastic cells, hematopoietic precursors, and several other cell types (Gougos et al., supra).
A cell surface antigen specific to vascular endothelium, referred to as endoGlyx-1 hereafter, has now been identified. This molecule is a glycoprotein with four subunits, bound together by disulfide bonds. The molecule appears to have a molecular weight in excess of 500 kd on SDS-PAGE under non-reducing conditions. Its four subunits, under reducing conditions, appear to have molecular weights of about 190 kd, 140 kd, 125 kd, and 110 kd. The antigen is described herein, as is a monoclonal antibody which specifically binds to it. Also disclosed are various diagnostic and therapeutic uses for the monoclonal antibody and the antigen.